The present invention relates to a down converter, and in particular to a low noise block down converter with integrated feedhorn (LNBF).
FIG. 1a is a schematic diagram showing a conventional LNBF. The LNBF 100 comprises a module frame 110, a first probe 120, a second probe 130, a connector 140, a first printed circuit board (not shown) and a second printed circuit board 155. The module frame 110 provides a waveguide tube 111, a first receiving portion 112 and a second receiving portion 113. The waveguide tube 111 is disposed on the module frame 110. The first and second receiving portions 112 and 113 are formed on the module frame 110. The first printed circuit board is installed in the module frame 110 and electronically connected to the second printed circuit board 155 and then connected to the connector 140 by a conducting wire 151. The first probe 120 is connected into the first receiving portion 112, a groove. The second probe 130 is connected into the second receiving portion 113. FIG. 1b is a cross section of the first probe 120 connected into the first receiving portion 112. The first probe 120 comprises a conducting wire 121 and an insulating material 122 wrapped around the conducting wire 121. The first probe 120 further comprises an abutting portion 123 contacting an edge of the first receiving portion 112. The first probe 120 is L-shaped.
The first receiving portion 112 is a groove to receive the L-shaped first probe 120. However, such a groove interrupts the inner surfaces of the waveguide tube 111 (acting as a resonance chamber). As a result, a deep notch 160 is generated in frequency response in the 12.6-12.7 GHz range, as shown in FIG. 1c, which reflects the signals received by the LNBF 100. The deep notch 160 is near the frequency band of the satellite signals processed by the LNBF 100, influencing the output of the LNBF 100.
In FIG. 1a, a height difference exists between the second printed circuit board 155 and the connector 140, whereby the conducting wire 151 is necessarily exposed to the air to connect the connector 140. Such an arrangement increases the large voltage standing wave rate (VSWR) beyond 4, thus significantly influence the received signals of the LNBF 100.
FIG. 1d is a circuit diagram of a conventional LNBF. The down converter circuit comprises a radio frequency circuit 2100 and an intermediate frequency circuit 2200. The frequency band of radio signals is between 10 GHz and 13 GHz. The frequency band of mid-frequency signals is between 900 MHz and 2500 MHz. The radio frequency circuit 2100 comprises an amplifier 210, filters 220, 221 and 222, a local oscillator 230, and a mixer 240. The intermediate frequency circuit 2200 comprises distribution units 261 and 262, a switch 270, and an amplifier 280. Conventionally, a plurality of radio frequency circuits 2100 and intermediate frequency circuits 2200 are alternately arranged on the first printed circuit board 150 and the second printed circuit board 155. To meet the requirements of radio frequency circuit 2100, both the first printed circuit board 150 and the second printed circuit board 155 are fabricated using material such as PTFE or Rogers, with high costs, accordingly.